Conventional liquid crystal displays are formed by bonding two substantially planar substrates, commonly referred to as a panel electrode, and a drive or signal substrate, together with a gap between them and then injecting a liquid crystal in the gap. Electrical connectivity between the drive and panel substrates is typically achieved with an anisotropic conductive film that connects wiring terminals on a flexible polyimide drive substrate with transparent electrode terminals formed on of indium tin oxide (ITO) is deposited on both the panel and drive substrates forming a patterned ITO layer on the substrate(s). After forming the patterned ITO layer, the two glass substrates are then bonded together with a known gap therebetween. To complete the manufacturing process of the LCD, a liquid crystal material is then vacuum filled in the gap of the bonded substrates thereby forming an active liquid crystal display.
U.S. Pat. No. 5,629,787, entitled “Method For Producing An LCD By Pressing The Substrates” by Tsubota et al., May 13, 1997, is illustrative of an existing process for making a typical liquid crystal display in which a spacer is used to determine the gap between the transparent substrates. Moreover, an ITO layer is coated only on one active surface of the transparent substrate. This reference, however, does not teach the presence of a plurality of adhesive filled, void-free vias formed in one of the substrates.
Canadian Patent Application No. 2,279,780, entitled “Light Density Control With LCD Arrangement” by Kraft, et al. filed Aug. 9, 1999, discloses a LCD arrangement with improved exposure control in a photo finishing environment in which multiple picture elements (pixels) associated with electrodes are positioned on bonded transparent plates and feed conductors to the electrodes feed control signals thereto. Referring to FIG. 1, a typical prior art LCD display element 1 contains vias 2 or feed throughs in a transparent substrate 3 and patterning of an ITO layer 6 on opposed active surfaces 4 and 5. Although the reference teaches vias 2 filled with an adhesive material layer 9 in the transparent substrate 3, the reference clearly recognizes that air bubbles or voids 8 exist in the adhesive material 9 filling the vias 2 that necessitates vacuum removal. Moreover, the reference does not recognize controlling the height and thickness of the adhesive material 9 as important factors in bonding a deck plate 7 to a transparent substrate 3 with an ITO coating layer 6 applied to the active surfaces 4, 5 or filling the vias 2.
U.S. Pat. No. 6,061,105, entitled “LCD With Via Connections Connecting The Data Line To A Conducting Line Both Before And Beyond The Sealing Material” by Nakagawa, May 9, 2000, discloses a liquid crystal display device that can eliminate an electrostatic discharge (ESD) problem resulting from a high dielectric constant filler that is appropriate for improved shape stability of a sealing material. While this reference is generally believed to teach a good solution to the electrostatic discharge problems encountered in the LCD display fabrication process, it does not teach or suggest adhesive filled, void-free vias formed in one of the substrates.
U.S. Pat. No. 6,061,105 discloses using vias connections in thin film transistors (TFT) connections. This reference, however, does not present vias in the transparent substrate that feed ITO from one active surface to an opposed active surface of the transparent substrate. According to the prior art reference, the vias are formed in the seal area and outside the active pixels area of the display. Thus, the reference does not contemplate the use of optical grade adhesives nor the need to maintain transparency in the active area. Hence this reference shows no appreciation for Applicants' problem or proposed solution.
Therefore, a need persists in the art for a liquid crystal display element and method of making same in which vias are formed in a substrate and then specially filled with an optical grade adhesive. The adhesive material filling the vias are virtually free of voids which substantially eliminates light scatter in an operating LCD, for instance, in a photofinishing application.